That's a real art & science kind of work:
the Basic incredients are an interesting photo idea, good sky, and celestial objects, a beautiful model and a matching terrestrial object/landscape for composition of the Astronude
the
pose of the model is crucial for the photo statement and effect like in a normal act photo
other than in case of a classical act photo, also the background BEHIND the model is as crucial as the pose for the photo statement and effect.You see
the influence of the background in the first photo below where Palm leaves seem to grow out of the boobies of the amazone, or in the sixth photo, where the model seems to be growing out from snow covered trees.
the starting point is a long exposure
astro photo set up using an astro mount, I personally prefer Astrotrac
then the model enters in the photo for a short part of the exposure time on a preselected spot in a preselected pose
LIGHT PAINTING: you work out the models body
using light, I call it light painting the body, this technique allows you to turn the focus on selected parts of the body, to leave out other parts, to produce shadings etc. You see the effect of light painting especially in the last two photos where
the boobies are worked out and the right arm of the model is left out
finally you have to take into account the shadow when light painting, see second photo